In the United States alone nosocomial bacteremia develops in about 194,000 patients per year, and of these about 75,000 die. Maki, D. G., 1981, Nosocomial Infect., (Dikson, R. E., Ed.), page 183, Yrke Medical Books, U.S.A. Most of these deaths are attributable to six major gram-negative bacilli--Pseudomonas aeruginosa, Escherichia coli, Proteus, Klebsiella, Enterobacter and Serratia. The current treatment for bacteremia is the administration of antibiotics which, have limited effectiveness in treatment of septic shock.
The precise pathology of bacteremia is not completely elucidated. Nevertheless, it is known that certain bacterial endotoxins called lipopolysaccharides (LPS), are the primary causative agent. LPS consists of at least three significant antigenic regions: lipid A; core polysaccharide; and O-specific polysaccharide. The latter is also referred to as O-specific chain or simply O-antigen. The O-specific chain region is a long-chain polysaccharide built up from repeating polysaccharide units. The number of polysaccharide units differs among different bacterial species and may vary from one to as many as six or seven monosaccharide units. While the O-specific chain varies among different gram-negative bacteria, the lipid A and core polysaccharides are similar if not identical.
Since LPS plays a key role in sepsis, many approaches have been pursued to neutralize its activity. Presently, there is considerable work which suggest that anti- LPS antibody will soon be a valuable clinical adjunct to the standard antibiotic therapy.
LPS initiates a cascade of biochemical events that eventually causes the death of the patient. It is widely believed that an early result of LPS introduction is the stimulation of macrophage cells and the production of tumor necrosis factor (TNF) as a result of LPS. Thus, considerable effort has been expended to produce neutralizing antibody to TNF, or other molecules that could inhibit its effects. It is likely that antibody to TNF will have valuable clinical applications. Tracey, et al., 1987, Nature, 330:662.
TNF has been shown to exist in both membrane-bound and soluble secreted forms. Decker, et al., 1987, J. of Immunol., 138:957; Kriegler, et al., 1988, Cell, 53:45. Human TNF has been cloned and shown to consist of a 17 kD polypeptide, plus an unusually long 76 amino acid putative signal leader sequence. The 17 kD molecule is a key agent involved in initiating the biochemical cascade responsible for sepsis. It has been proposed by Kriegler, et al., 1988, Cell, 53:45, that TNF may exist as both a membrane bound 26 kD form, and a soluble form corresponding to the 17 kD species. The 26 kD form is the precursor, or prohormone, of the mature 17 kD molecule. It has further been proposed by Kriegler, et al. above, that the two forms of TNF may have different biological effects, primarily as a result of differences in tissue distribution.
It will be appreciated that because TNF plays a key role in causing sepsis and other diseases that there is a need to identify and develop anti-TNF prophylactics/therapeutics. As mentioned above, anti-TNF antibody appears to be promising, and has been shown to be effective in baboons. However, these studies have involved the use of non-human TNF and non-human TNF antibody. From a practical standpoint non-human anti-TNF antibody will have limited therapeutic application because of immunologic rejection of the antibody by a patient's immune system. Consequently, a human antibody, or a genetically engineered antibody consisting of the human constant region and the mouse variable region ("humanized antibody") is preferred.
TNF, in addition to playing a critical role in sepsis, has recently been shown to be involved in initiating the expression of human immunodeficiency virus in human cells that carry latent virus. Folks et al., 1989, PNAS (USA), 86:2365. Thus, preventing or inhibiting the formation of the 17 kD, or lower molecular weight forms of TNF might be a valuable prophylactic for the treatment of AIDS patients by preventing the expression of virus that is latent in the patient.
TNF also plays a role in various autoimmune diseases, particularly rheumatoid arthritis. Duff, et al., 1987, International Conference on Tumor Necrosis Factor and Related Cytotoxins, 175:10. Thus, compounds or methods for inhibiting TNF action will have considerable application for the treatment of a variety of diseases of immunologic origin.
In addition to antibody, other molecules with TNF inhibitory activity are being sought. Non-antibody TNF inhibitors are described by Seckinger, et al., 1988, J. Exp. Med., 167:151, and Seckinger, et al, 1989, J. Biol. Chem,. 264:11966, and in European Patent Application No. 88830365.8, inventors Wallach, et al. The inhibitors are present in the urine of febrile patients, and have been purified and shown to have molecular weights of about 27,000-33,000. These inhibitors are now known to be soluble forms of the TNF receptor. Although these molecules exhibit TNF-inhibitory activity, neither of the inhibitors has yet been shown to be effective in the treatment of sepsis in humans.
From the foregoing discussion it is apparent that there is a need to identify and develop additional anti-TNF inhibitors, both antibody based or otherwise, that are efficacious in the treatment of sepsis.